Proper segregation of genetic material during cell division is critical and depends on the formation and stability of the bipolar mitotic spindle composed of microtubules and associated proteins. Aneuploid cells resulting from mis-segregation suffer detrimental effects and reduced viability as observed in cancers and genetic diseases. The Saccharomyces cerevisiae protein Stulp interacts with microtubules, localizes to the mitotic spindle midzone region, and is essential for proper spindle structure and viability. However, proteins that interact with Stu1 and the role of Stu1p in formation and maintenance of the mitotic spindle is not understood. Identification of Stu1 associating proteins using Tandem Affinity Purification (TAP) and mass spectroscopy will aid in understanding the context of Stu1 in the spindle: Yeast is a valuable genetic system, but in depth biochemistry is limited. Xenopus laevis egg extracts are a powerful in vitro system for studying spindle formation and microtubule dynamics. Immunolocalization and immunodepletion of extracts using antibodies against a Xenopus protein identified from cDNA libraries encoding a Stu1 homologue will allow analysis of this class of proteins in bipolar spindle formation and microtubule dynamics.